discovered_01_2013

discovered 01.13 FOCUS WWW.Hzdr.DE FASTER PROCESSORS: Tiny defects speed up the switching processes of computers and mobile phones. These holes or imperfections lend themselves extremely well to study at the EPOS positron source to yield important clues for improving modern materials. Photo: edelweiss – fotolia.com _TEXT . Roland Knauer Defects for the future // Positron source EPOS measures irregularities in semiconductors, solar cells & Co. Whenever Andreas Wagner of the Institute of Radiation Physics at the Helmholtz-Zentrum Dresden-Rossendorf says he is interested in defects, he usually provokes confused looks on the part of lay people. Solid state physicists, on the other hand, know immediately what he’s talking about: minute defects in solids, like when individual atoms have gone missing. Such defects influence the properties of materials like solar cells but they can be examined only with great difficulty. Andreas Wagner is the man in charge of the positron facility EPOS, which allows for the analysis of solid state defects. To better understand this method, let’s take a closer look at the structure of atoms. The atomic nucleus is made up of positively charged protons and uncharged neutrons. At a considerable distance from the nucleus, the significantly smaller-sized electrons, which carry a negative electrical charge, are orbiting about the atomic nucleus. Normally, the number of electrons equals the number of protons in the nucleus so that their charges cancel each other out, giving the atom an overall net charge of zero. If, because of some defect, an atom gets lost from a solid, the positively charged atomic nucleus is now missing, which leads to re-arrangement of the electrons. As such, there are a few more electrons in the defect’s immediate vicinity than in the undisturbed areas. "In these types of defects, the missing tiny positive electrical charge acts like a vacuum

discovered_01_2013

Pages